Associations Between Serum Iodine Concentration And Iodine Status And Thyroid Function In Children And Pregnant Women

Objective: This study aims to figure out how serum iodine interacts with iodine intake and the relationship between serum iodine concentration and thyroid function,and to explore the utility of serum iodine to evaluate individual iodine status in school aged children.After that,this study intends to clarify if there is relationship between serum iodine concentration and thyroid function in pregnant women and then to discover whether serum iodine concentration during pregnancy influences postpartum unrine iodine concentration(UIC),breastmilk iodine concentration(BMIC),UIC and thyroid stimulating hormone(TSH)of their infants.Method: During October 2013 and May 2015,randomized cluster sampling was used to determine 7-14 y old children.Height and weight were recorded,and thyroid volume(Tvol)was measured by type B ultra-sound while fasting venous blood sample and 24-h unrine sample were obtained.Another 24-h urine sample was collected one month later.Serum total iodine(St I),non-protein bound iodine(Snb I),free triiodothyroinine(f T3),free thyroxine(f T4),TSH,thyroglobulin(Tg),UIC were determined and urine iodine excretion(UIE),urine iodine to creatinine ratio(UI/Cr)and average daily iodine intake were calculated.After that,pregnant women were recruited between Apirl 2015 and December 2018 in Tanggu Obstetrics and Gynecology Hospital,Tianjin,and Gaoqing Maternal and Child Health Care Hospital,Shandong.Gestational age,height and weight were recorded,and Tvol was measured while fasting venous blood sample and spot sample were obtained.After delivery,women from Tanggu were followed-up and breast milk,urine of the mothers and infants,dried blood spot of the newborns were collected.St I,Snb I,f T3,f T4,TSH,thyroglobulin antibody(Tg Ab),Tg,UIC,thyroid peroxidase antibody(TPOAb),and breast milk concentration(BMIC)were measured.Associations between serum iodine and others were analyzed.Results: 1686 children were enrolled in this study.The mean age was 10.7 ± 1.4 year.The median St I was 97.0 μg/L(IQR: 83.3-113)and the median Snb I was 54.1 μg/L(IQR: 45.4-65.7).Differences between boys and girls were statistically significant(P<0.05).St I and Snb I were both reversly correlated with body mass index(BMI) (P<0.05),but were positively correlated with f T4,TSH,Tg,24-h UIC,24-h UIE,UI/Cr and the average daily iodine intake.A “U” shape curve was detected between goiter rates asn St I.Goiter rate was below 5% in children with St I between 60-79 μg/L.Meanwhile,children having St I of 60-69 μg/L had the smallest Tvol.The area under curve(AUC)of St I and Snb I for diagnosing excessive iodine intake were 0.76 and 0.77 respectively.1396 pregnant women were recruited in this study and the mean age was 29.1 ± 3.8 year.The median St I was 107 μg/L(IQR: 94.1-122)while the median Snb I was 57.0 μg/L(IQR: 48.5-65.5).They both declined across gestational week(P<0.05).St I and Snb I were both nagetively correlated with TSH(P<0.05)but were positively correlated with f T3,f T4,UIC(P<0.05).Snb I were positively correlated with UI/Cr(r= 0.16,P<0.001).When St I was lower than the 10 th percentile,the risk of having UIC<150 μg/L was 1.72(95% CI: 1.21,2.45)times,while the risk of having hypothyroxine was 3.23(95% CI: 1.91,5.48)times.However,when St I was higher than the 90 th percentile,the risk of having UIC>500 μg/L and thyrotoxicosis were 2.05(95% CI: 1.21,3.49)and 14.43(95% CI: 5.06,41.18)times respectively.On the other hand,when Snb I of pregnant women was less than the 10 th percentile,the risk of having hypothyroxine was 2.79(95% CI: 1.62,4.80)times higher compared with the others.When their Snb I was greater than the 90 th percentile,the risk of having UIC>500 μg/L and thyrotoxicosis were 3.06(95% CI: 1.88,4.98)and 14.43(95% CI: 5.06,41.18)times higher repectively When St I during pregnancy was less than 94.1 μg/L,UI/Cr at 4 weeks postpartum was lower than the others(P=0.0042).When Snb I was less than 48.5 μg/L,UIC at 1 week and UI/Cr at 4 weeks postpartum was lower than the others(P<0.05).When Snb I during pregnancy was higher than 65.5μg/L,UI/Cr at 8 weeks postpartum was lower(P=0.044).Snb I in pregnancy was nagtively correlated with BMIC at 8 weeks(r=-0.19,P=0.031).St I and Snb I were both nagetively correlated with their infants’ UIC at the age of 8 weeks(P<0.05).